In a UMTS (Universal Mobile Telecommunication System) network, an LTE (Long Term Evolution) has been specified with the aim to further increase the data rate and reduce the latency (Non-Patent Document 1). An LTE-advanced has been specified with the aim to further broaden the frequency band and increase the data rate from the LTE, and a successor system of the LTE called 5G (5th generation mobile communication system), for example has been discussed.
LTE Rel.8 to 12 have been specified assuming that exclusive operations are performed in a frequency band (that is, a licensed band) permitted to a business operator. For example, 800 MHz, 2 GHz, or 1.8 GHz is used as the licensed band.
A wide spread of high-functionality user equipments such as smartphones or tablets has increased user traffic rapidly. To absorb this increasing user traffic, although it is necessary to add additional frequency bands, there is a limit on the licensed band spectrum (licensed spectrum). Due to this, expanding the frequencies of an LTE system using an available unlicensed spectrum band (this is referred to as an unlicensed band) other than the licensed band has been discussed (Non-Patent Document 2). For example, 2.4 GHz or 5 GHz as used by Wi-Fi (registered trademark) is used as the unlicensed band. LTE Rel.13 discusses CA (Carrier Aggregation) to be performed between the licensed band and the unlicensed band as illustrated in FIG. 1. In this manner, communication performed using the unlicensed band together with the licensed band is referred to as LAA (License-Assisted Access). In future, dual connectivity of the licensed band and the unlicensed band and standalone of the unlicensed band will be the subject to be discussed in LAA.